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Diversity of RPA190 in Phytophthora infestans resistant to metalaxyl

Fengping Chen: Fujian Agriculture and Forestry University

<div>Metalaxyl is a phenylamide fungicide, introduced for oomycete management since 1970s. The <em>RPA190</em> gene, the largest subunit of RNA polymerase I, was indicated recently involved in metalaxyl resistance. The present study described the metalaxyl resistance and diversity of <em>RPA190</em> in <em>Phytophthora infestans </em>collected consecutively in three years from Yunnan province in China. All isolates were resistant to metalaxyl, whose EC<sub>50</sub> values greater than 5 µg/ml. The difference in sensitivity between the isolates at each end of the spectrum was more than seven folds. Metalaxyl sensitivity tended to decrease over sampling time for isolates collected in 2012, 2103, and 2014, respectively. The nucleotide diversity in the three temporal populations ranged from 0.00273 to 0.00282 with an overall diversity of 0.00273 when sequences from the three years were combined. The haplotype diversity in the three years ranged from 0.787 to 0.828 with an overall diversity of 0.776 when sequences from the three years were pooled. Haplotype diversity directionally increased over temporal scale but the correlation between sampling year and haplotype diversity was not significant. The nucleotide sequences of haplotypes clustered into six clades with five mutations were shown to be under positive selection. The study indicated high diversity of RPA190 gene in metalaxyl resistant <em>P. infestans</em>.</div>